Friction Stir Welding Steel Sheets Preheating Method
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Solution Overview
Problem
Conventional friction stir welding methods for steel sheets face challenges in achieving high-speed welding without defects and minimizing tool damage, as existing techniques often result in inadequate softening and uneven heat distribution between the front and back surfaces.
Innovation Solution
The method involves using a pair of heating devices to control temperature distribution on both surfaces of the steel sheets before welding, ensuring a temperature difference within a specific range to facilitate uniform welding and prevent defects, while also managing the cooling and re-heating processes to prevent cracking in high-C steel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If friction stir welding is performed at high welding speed, then productivity is improved, but welding defects occur due to inadequate softening of the steel sheets
Solution Approach 1:
The patent applies preliminary heating action by using a heating device to heat the steel sheets before friction stir welding begins. This pre-heating ensures the steel sheets reach the appropriate temperature for softening, enabling high-speed welding without compromising weld quality. The heating device is positioned to heat the welding area in advance, so when the rotating tool arrives, the material is already in the optimal state for plastic flow and bonding.
2Productivity
If heating is applied to accelerate welding, then productivity is improved, but uneven temperature distribution occurs between front and back surfaces
Solution Approach 1:
The patent implements local quality control by using heating devices on both the front and back surfaces of the steel sheets. This dual-sided heating arrangement ensures uniform temperature distribution across the thickness of the material. The heating devices are positioned and controlled to maintain substantially equal temperatures on both surfaces, preventing thermal gradients that would cause uneven softening and welding defects.
3Productivity
If high-C steel is welded using conventional methods, then productivity is maintained, but cracking and embrittlement occur due to rapid cooling
Solution Approach 1:
The patent converts the harmful rapid cooling effect into a beneficial process by implementing a controlled cooling system. After high-speed friction stir welding of high-C steel, the controlled cooling system manages the cooling rate to prevent martensitic transformation and associated cracking. The system maintains the weld area at elevated temperature longer, allowing slower, more controlled cooling that avoids embrittlement while preserving the high productivity benefits of fast welding.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables high-speed welding of steel sheets with reduced risk of defects and tool damage, achieving stable joints with controlled bead width and minimizing embrittlement and cracking issues.
Implementation Method 1
using a pair of heating devices to control temperature distribution on both surfaces of the steel sheets before welding
Implementation Method 2
utilizing the softening of the working materials caused by the frictional heat generated between the rotating tool and the working materials
Data Source
Figure 1~2
Figure 3
Figure 4(a)~4(b)
AI summary
Provided is a friction stir welding method for steel sheets comprising: inserting a rotating tool into an unwelded portion where two or more steel sheets are overlapped or butted together; moving the rotating tool along portions to be welded while rotating the tool, so that a softened portion is formed in the steel sheets by friction heat generated between the rotating tool and the steel sheets, and the steel sheets are welded together by utilizing a plastic flow generated by the softened portion being stirred; and preheating the unwelded portion before welding by the rotating tool, wherein the preheating of the unwelded portion is performed by a pair of heating devices disposed over and under the unwelded portion and ahead of the rotating tool in the advancing direction to enable high speed welding without the risk of generation of welding defects and damages to the welding tool.